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			<h1>Java MySQL 连接
</h1>
<p>本章节我们为大家介绍 Java 如何使用 使用 JDBC 连接 MySQL 数据库。</p>
<p>Java 连接 MySQL 需要驱动包，最新版下载地址为：<strong><a href="http://dev.mysql.com/downloads/connector/j/" target="_blank" rel="noopener noreferrer">http://dev.mysql.com/downloads/connector/j/</a></strong>，解压后得到 jar 库文件，然后在对应的项目中导入该库文件。</p>
<p><img decoding="async" src="https://www.runoob.com/wp-content/uploads/2016/08/38EF259A-CC97-4001-96AD-C6648BE2A4F4.jpg"></p>
<p>你可以下载本站提供的 jar 包：<strong><a href="http://static.runoob.com/download/mysql-connector-java-5.1.39-bin.jar" target="_blank" rel="noopener noreferrer">mysql-connector-java-5.1.39-bin.jar</a></strong></p>
<p>本实例使用的是 Eclipse，导入 jar 包：</p>
<p><img decoding="async" src="//www.runoob.com/wp-content/uploads/2013/12/191E2E30-DD23-41C8-A419-DFEAEAE06BF6.jpg" width="40%"></p>


<blockquote><p><strong>MySQL 8.0 以上版本的数据库连接有所不同：</strong></p>
<ul><li>
<p>1、MySQL 8.0 以上版本驱动包版本 <a href="https://static.runoob.com/download/mysql-connector-java-8.0.16.jar">mysql-connector-java-8.0.16.jar</a>。</p></li><li>
<p>2、<strong>com.mysql.jdbc.Driver</strong> 更换为 <span class="marked">com.mysql.cj.jdbc.Driver</span>。</p></li><li>

<p>MySQL 8.0 以上版本不需要建立 SSL 连接的，需要显示关闭。</p></li><li>
<p>allowPublicKeyRetrieval=true 允许客户端从服务器获取公钥。</p></li>
<li>
<p>最后还需要设置 CST。</p>
</li></ul>

<p>加载驱动与连接数据库方式如下：</p>
<pre>Class.forName("com.mysql.cj.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test_demo?useSSL=false&amp;allowPublicKeyRetrieval=true&amp;serverTimezone=UTC","root","password");</pre></blockquote>



<hr>
<h2>创建测试数据</h2>
<p>接下来我们在 MySQL 中创建 RUNOOB 数据库，并创建 websites 数据表，表结构如下：</p>
<div class="example">
<div class="example_code">
<div class="hl-main"><span class="hl-reserved">CREATE</span><span class="hl-code"> </span><span class="hl-reserved">TABLE</span><span class="hl-code"> </span><span class="hl-quotes">`</span><span class="hl-identifier">websites</span><span class="hl-quotes">`</span><span class="hl-code"> </span><span class="hl-brackets">(</span><span class="hl-code">
  </span><span class="hl-quotes">`</span><span class="hl-identifier">id</span><span class="hl-quotes">`</span><span class="hl-code"> </span><span class="hl-reserved">int</span><span class="hl-brackets">(</span><span class="hl-number">11</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-reserved">NOT</span><span class="hl-code"> </span><span class="hl-reserved">NULL</span><span class="hl-code"> </span><span class="hl-identifier">AUTO_INCREMENT</span><span class="hl-code">,
  </span><span class="hl-quotes">`</span><span class="hl-identifier">name</span><span class="hl-quotes">`</span><span class="hl-code"> </span><span class="hl-reserved">char</span><span class="hl-brackets">(</span><span class="hl-number">20</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-reserved">NOT</span><span class="hl-code"> </span><span class="hl-reserved">NULL</span><span class="hl-code"> </span><span class="hl-reserved">DEFAULT</span><span class="hl-code"> </span><span class="hl-quotes">'</span><span class="hl-quotes">'</span><span class="hl-code"> </span><span class="hl-identifier">COMMENT</span><span class="hl-code"> </span><span class="hl-quotes">'</span><span class="hl-string">站点名称</span><span class="hl-quotes">'</span><span class="hl-code">,
  </span><span class="hl-quotes">`</span><span class="hl-identifier">url</span><span class="hl-quotes">`</span><span class="hl-code"> </span><span class="hl-reserved">varchar</span><span class="hl-brackets">(</span><span class="hl-number">255</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-reserved">NOT</span><span class="hl-code"> </span><span class="hl-reserved">NULL</span><span class="hl-code"> </span><span class="hl-reserved">DEFAULT</span><span class="hl-code"> </span><span class="hl-quotes">'</span><span class="hl-quotes">'</span><span class="hl-code">,
  </span><span class="hl-quotes">`</span><span class="hl-identifier">alexa</span><span class="hl-quotes">`</span><span class="hl-code"> </span><span class="hl-reserved">int</span><span class="hl-brackets">(</span><span class="hl-number">11</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-reserved">NOT</span><span class="hl-code"> </span><span class="hl-reserved">NULL</span><span class="hl-code"> </span><span class="hl-reserved">DEFAULT</span><span class="hl-code"> </span><span class="hl-quotes">'</span><span class="hl-string">0</span><span class="hl-quotes">'</span><span class="hl-code"> </span><span class="hl-identifier">COMMENT</span><span class="hl-code"> </span><span class="hl-quotes">'</span><span class="hl-string">Alexa 排名</span><span class="hl-quotes">'</span><span class="hl-code">,
  </span><span class="hl-quotes">`</span><span class="hl-identifier">country</span><span class="hl-quotes">`</span><span class="hl-code"> </span><span class="hl-reserved">char</span><span class="hl-brackets">(</span><span class="hl-number">10</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-reserved">NOT</span><span class="hl-code"> </span><span class="hl-reserved">NULL</span><span class="hl-code"> </span><span class="hl-reserved">DEFAULT</span><span class="hl-code"> </span><span class="hl-quotes">'</span><span class="hl-quotes">'</span><span class="hl-code"> </span><span class="hl-identifier">COMMENT</span><span class="hl-code"> </span><span class="hl-quotes">'</span><span class="hl-string">国家</span><span class="hl-quotes">'</span><span class="hl-code">,
  </span><span class="hl-reserved">PRIMARY</span><span class="hl-code"> </span><span class="hl-reserved">KEY</span><span class="hl-code"> </span><span class="hl-brackets">(</span><span class="hl-quotes">`</span><span class="hl-identifier">id</span><span class="hl-quotes">`</span><span class="hl-brackets">)</span><span class="hl-code">
</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-identifier">ENGINE</span><span class="hl-code">=</span><span class="hl-identifier">InnoDB</span><span class="hl-code"> </span><span class="hl-identifier">AUTO_INCREMENT</span><span class="hl-code">=</span><span class="hl-number">10</span><span class="hl-code"> </span><span class="hl-reserved">DEFAULT</span><span class="hl-code"> </span><span class="hl-identifier">CHARSET</span><span class="hl-code">=</span><span class="hl-identifier">utf8</span><span class="hl-code">;</span></div>
</div>
</div>
<p>插入一些数据：</p>
<div class="example">
<div class="example_code">
<div class="hl-main"><span class="hl-reserved">INSERT</span><span class="hl-code"> </span><span class="hl-reserved">INTO</span><span class="hl-code"> </span><span class="hl-quotes">`</span><span class="hl-identifier">websites</span><span class="hl-quotes">`</span><span class="hl-code"> </span><span class="hl-reserved">VALUES</span><span class="hl-code"> </span><span class="hl-brackets">(</span><span class="hl-quotes">'</span><span class="hl-string">1</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">Google</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">https://www.google.cm/</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">1</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">USA</span><span class="hl-quotes">'</span><span class="hl-brackets">)</span><span class="hl-code">, </span><span class="hl-brackets">(</span><span class="hl-quotes">'</span><span class="hl-string">2</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">淘宝</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">https://www.taobao.com/</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">13</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">CN</span><span class="hl-quotes">'</span><span class="hl-brackets">)</span><span class="hl-code">, </span><span class="hl-brackets">(</span><span class="hl-quotes">'</span><span class="hl-string">3</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">菜鸟教程</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">http://www.runoob.com</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">5892</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-quotes">'</span><span class="hl-brackets">)</span><span class="hl-code">, </span><span class="hl-brackets">(</span><span class="hl-quotes">'</span><span class="hl-string">4</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">微博</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">http://weibo.com/</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">20</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">CN</span><span class="hl-quotes">'</span><span class="hl-brackets">)</span><span class="hl-code">, </span><span class="hl-brackets">(</span><span class="hl-quotes">'</span><span class="hl-string">5</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">Facebook</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">https://www.facebook.com/</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">3</span><span class="hl-quotes">'</span><span class="hl-code">, </span><span class="hl-quotes">'</span><span class="hl-string">USA</span><span class="hl-quotes">'</span><span class="hl-brackets">)</span><span class="hl-code">;</span></div>
</div>
</div>
<p>数据表显示如下：</p>
<p><img decoding="async" src="//www.runoob.com/wp-content/uploads/2013/12/mysql-data.jpg"></p><hr>
<h2>连接数据库</h2>
<p>以下实例使用了 JDBC 连接 MySQL 数据库，注意一些数据如用户名，密码需要根据你的开发环境来配置：</p>
<div class="example">
<h2 class="example">MySQLDemo.java 文件代码：</h2>
<div class="example_code">
<div class="hl-main"><span class="hl-reserved">package</span><span class="hl-code"> </span><span class="hl-identifier">com</span><span class="hl-code">.</span><span class="hl-identifier">runoob</span><span class="hl-code">.</span><span class="hl-identifier">test</span><span class="hl-code">;
 
</span><span class="hl-reserved">import</span><span class="hl-code"> </span><span class="hl-identifier">java</span><span class="hl-code">.</span><span class="hl-identifier">sql</span><span class="hl-code">.*;
 
</span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-reserved">class</span><span class="hl-code"> </span><span class="hl-identifier">MySQLDemo</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
 
    </span><span class="hl-comment">//</span><span class="hl-comment"> MySQL 8.0 以下版本 - JDBC 驱动名及数据库 URL</span><span class="hl-comment"></span><span class="hl-code">
    </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">final</span><span class="hl-code"> </span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-identifier">JDBC_DRIVER</span><span class="hl-code"> = </span><span class="hl-quotes">&quot;</span><span class="hl-string">com.mysql.jdbc.Driver</span><span class="hl-quotes">&quot;</span><span class="hl-code">;  
    </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">final</span><span class="hl-code"> </span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-identifier">DB_URL</span><span class="hl-code"> = </span><span class="hl-quotes">&quot;</span><span class="hl-string">jdbc:mysql://localhost:3306/RUNOOB</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
 
    </span><span class="hl-comment">//</span><span class="hl-comment"> MySQL 8.0 以上版本 - JDBC 驱动名及数据库 URL</span><span class="hl-comment"></span><span class="hl-code">
    </span><span class="hl-comment">//</span><span class="hl-comment">static final String JDBC_DRIVER = &quot;com.mysql.cj.jdbc.Driver&quot;;  </span><span class="hl-comment"></span><span class="hl-code">
    </span><span class="hl-comment">//</span><span class="hl-comment">static final String DB_URL = &quot;jdbc:mysql://localhost:3306/RUNOOB?useSSL=false&amp;allowPublicKeyRetrieval=true&amp;serverTimezone=UTC&quot;;</span><span class="hl-comment"></span><span class="hl-code">
 
 
    </span><span class="hl-comment">//</span><span class="hl-comment"> 数据库的用户名与密码，需要根据自己的设置</span><span class="hl-comment"></span><span class="hl-code">
    </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">final</span><span class="hl-code"> </span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-identifier">USER</span><span class="hl-code"> = </span><span class="hl-quotes">&quot;</span><span class="hl-string">root</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
    </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">final</span><span class="hl-code"> </span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-identifier">PASS</span><span class="hl-code"> = </span><span class="hl-quotes">&quot;</span><span class="hl-string">123456</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
 
    </span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">void</span><span class="hl-code"> </span><span class="hl-identifier">main</span><span class="hl-brackets">(</span><span class="hl-identifier">String</span><span class="hl-brackets">[</span><span class="hl-brackets">]</span><span class="hl-code"> </span><span class="hl-identifier">args</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
        </span><span class="hl-identifier">Connection</span><span class="hl-code"> </span><span class="hl-identifier">conn</span><span class="hl-code"> = </span><span class="hl-reserved">null</span><span class="hl-code">;
        </span><span class="hl-identifier">Statement</span><span class="hl-code"> </span><span class="hl-identifier">stmt</span><span class="hl-code"> = </span><span class="hl-reserved">null</span><span class="hl-code">;
        </span><span class="hl-reserved">try</span><span class="hl-brackets">{</span><span class="hl-code">
            </span><span class="hl-comment">//</span><span class="hl-comment"> 注册 JDBC 驱动</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-identifier">Class</span><span class="hl-code">.</span><span class="hl-identifier">forName</span><span class="hl-brackets">(</span><span class="hl-identifier">JDBC_DRIVER</span><span class="hl-brackets">)</span><span class="hl-code">;
        
            </span><span class="hl-comment">//</span><span class="hl-comment"> 打开链接</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">连接数据库...</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">conn</span><span class="hl-code"> = </span><span class="hl-identifier">DriverManager</span><span class="hl-code">.</span><span class="hl-identifier">getConnection</span><span class="hl-brackets">(</span><span class="hl-identifier">DB_URL</span><span class="hl-code">,</span><span class="hl-identifier">USER</span><span class="hl-code">,</span><span class="hl-identifier">PASS</span><span class="hl-brackets">)</span><span class="hl-code">;
        
            </span><span class="hl-comment">//</span><span class="hl-comment"> 执行查询</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string"> 实例化Statement对象...</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">stmt</span><span class="hl-code"> = </span><span class="hl-identifier">conn</span><span class="hl-code">.</span><span class="hl-identifier">createStatement</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-identifier">sql</span><span class="hl-code">;
            </span><span class="hl-identifier">sql</span><span class="hl-code"> = </span><span class="hl-quotes">&quot;</span><span class="hl-string">SELECT id, name, url FROM websites</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
            </span><span class="hl-identifier">ResultSet</span><span class="hl-code"> </span><span class="hl-identifier">rs</span><span class="hl-code"> = </span><span class="hl-identifier">stmt</span><span class="hl-code">.</span><span class="hl-identifier">executeQuery</span><span class="hl-brackets">(</span><span class="hl-identifier">sql</span><span class="hl-brackets">)</span><span class="hl-code">;
        
            </span><span class="hl-comment">//</span><span class="hl-comment"> 展开结果集数据库</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-reserved">while</span><span class="hl-brackets">(</span><span class="hl-identifier">rs</span><span class="hl-code">.</span><span class="hl-identifier">next</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-brackets">{</span><span class="hl-code">
                </span><span class="hl-comment">//</span><span class="hl-comment"> 通过字段检索</span><span class="hl-comment"></span><span class="hl-code">
                </span><span class="hl-types">int</span><span class="hl-code"> </span><span class="hl-identifier">id</span><span class="hl-code">  = </span><span class="hl-identifier">rs</span><span class="hl-code">.</span><span class="hl-identifier">getInt</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">id</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
                </span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-identifier">name</span><span class="hl-code"> = </span><span class="hl-identifier">rs</span><span class="hl-code">.</span><span class="hl-identifier">getString</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">name</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
                </span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-identifier">url</span><span class="hl-code"> = </span><span class="hl-identifier">rs</span><span class="hl-code">.</span><span class="hl-identifier">getString</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">url</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
    
                </span><span class="hl-comment">//</span><span class="hl-comment"> 输出数据</span><span class="hl-comment"></span><span class="hl-code">
                </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">print</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">ID: </span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">id</span><span class="hl-brackets">)</span><span class="hl-code">;
                </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">print</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">, 站点名称: </span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">name</span><span class="hl-brackets">)</span><span class="hl-code">;
                </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">print</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">, 站点 URL: </span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">url</span><span class="hl-brackets">)</span><span class="hl-code">;
                </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">print</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-special">\n</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-brackets">}</span><span class="hl-code">
            </span><span class="hl-comment">//</span><span class="hl-comment"> 完成后关闭</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-identifier">rs</span><span class="hl-code">.</span><span class="hl-identifier">close</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">stmt</span><span class="hl-code">.</span><span class="hl-identifier">close</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">conn</span><span class="hl-code">.</span><span class="hl-identifier">close</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
        </span><span class="hl-brackets">}</span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-identifier">SQLException</span><span class="hl-code"> </span><span class="hl-identifier">se</span><span class="hl-brackets">)</span><span class="hl-brackets">{</span><span class="hl-code">
            </span><span class="hl-comment">//</span><span class="hl-comment"> 处理 JDBC 错误</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-identifier">se</span><span class="hl-code">.</span><span class="hl-identifier">printStackTrace</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
        </span><span class="hl-brackets">}</span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-identifier">Exception</span><span class="hl-code"> </span><span class="hl-identifier">e</span><span class="hl-brackets">)</span><span class="hl-brackets">{</span><span class="hl-code">
            </span><span class="hl-comment">//</span><span class="hl-comment"> 处理 Class.forName 错误</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-identifier">e</span><span class="hl-code">.</span><span class="hl-identifier">printStackTrace</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
        </span><span class="hl-brackets">}</span><span class="hl-reserved">finally</span><span class="hl-brackets">{</span><span class="hl-code">
            </span><span class="hl-comment">//</span><span class="hl-comment"> 关闭资源</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-reserved">try</span><span class="hl-brackets">{</span><span class="hl-code">
                </span><span class="hl-reserved">if</span><span class="hl-brackets">(</span><span class="hl-identifier">stmt</span><span class="hl-code">!=</span><span class="hl-reserved">null</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-identifier">stmt</span><span class="hl-code">.</span><span class="hl-identifier">close</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-brackets">}</span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-identifier">SQLException</span><span class="hl-code"> </span><span class="hl-identifier">se2</span><span class="hl-brackets">)</span><span class="hl-brackets">{</span><span class="hl-code">
            </span><span class="hl-brackets">}</span><span class="hl-comment">//</span><span class="hl-comment"> 什么都不做</span><span class="hl-comment"></span><span class="hl-code">
            </span><span class="hl-reserved">try</span><span class="hl-brackets">{</span><span class="hl-code">
                </span><span class="hl-reserved">if</span><span class="hl-brackets">(</span><span class="hl-identifier">conn</span><span class="hl-code">!=</span><span class="hl-reserved">null</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-identifier">conn</span><span class="hl-code">.</span><span class="hl-identifier">close</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-brackets">}</span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-identifier">SQLException</span><span class="hl-code"> </span><span class="hl-identifier">se</span><span class="hl-brackets">)</span><span class="hl-brackets">{</span><span class="hl-code">
                </span><span class="hl-identifier">se</span><span class="hl-code">.</span><span class="hl-identifier">printStackTrace</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-brackets">}</span><span class="hl-code">
        </span><span class="hl-brackets">}</span><span class="hl-code">
        </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">Goodbye!</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
    </span><span class="hl-brackets">}</span><span class="hl-code">
</span><span class="hl-brackets">}</span></div>
</div>
</div>
<p>以上实例执行输出结果如下：</p>
<p><img decoding="async" src="//www.runoob.com/wp-content/uploads/2016/08/result.jpg" width="70%"></p>			<!-- 其他扩展 -->
						
			</div>
			
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		<!-- 笔记列表 -->
		<style>
.wrapper {
  /*text-transform: uppercase; */
  background: #ececec;
  color: #555;
  cursor: help;
  font-family: "Gill Sans", Impact, sans-serif;
  font-size: 20px;
  position: relative;
  text-align: center;
  width: 200px;
  -webkit-transform: translateZ(0); /* webkit flicker fix */
  -webkit-font-smoothing: antialiased; /* webkit text rendering fix */
}

.wrapper .tooltip {
  white-space: nowrap;
  font-size: 14px;
  text-align: left;
  background: #96b97d;
  bottom: 100%;
  color: #fff;
  display: block;
  left: -25px;
  margin-bottom: 15px;
  opacity: 0;
  padding: 14px;
  pointer-events: none;
  position: absolute;
  
  -webkit-transform: translateY(10px);
     -moz-transform: translateY(10px);
      -ms-transform: translateY(10px);
       -o-transform: translateY(10px);
          transform: translateY(10px);
  -webkit-transition: all .25s ease-out;
     -moz-transition: all .25s ease-out;
      -ms-transition: all .25s ease-out;
       -o-transition: all .25s ease-out;
          transition: all .25s ease-out;
  -webkit-box-shadow: 2px 2px 6px rgba(0, 0, 0, 0.28);
     -moz-box-shadow: 2px 2px 6px rgba(0, 0, 0, 0.28);
      -ms-box-shadow: 2px 2px 6px rgba(0, 0, 0, 0.28);
       -o-box-shadow: 2px 2px 6px rgba(0, 0, 0, 0.28);
          box-shadow: 2px 2px 6px rgba(0, 0, 0, 0.28);
}
.tooltip a {
	color:#fff;
}
/* This bridges the gap so you can mouse into the tooltip without it disappearing */
.wrapper .tooltip:before {
  bottom: -20px;
  content: " ";
  display: block;
  height: 20px;
  left: 0;
  position: absolute;
  width: 100%;
}  

/* CSS Triangles - see Trevor's post */
.wrapper .tooltip:after {
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		<li class="comment byuser comment-author-tianqixin bypostauthor even thread-even depth-1" id="comment-27029"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;哈哈哈哈哈。。。呃~</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;248***8117@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="../design-pattern/data-access-object-pattern.html">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-27029" data-commid = "27029" class="upvotejs"><a class="upvote"></a> <span class="count">77</span></div></div><div class="comt-main" id="div-comment-27029"><p data-title="Java DAO 模式"><strong>DAO 模式</strong></p>
<p>DAO (DataAccessobjects 数据存取对象)是指位于业务逻辑和持久化数据之间实现对持久化数据的访问。通俗来讲，就是将数据库操作都封装起来。</p>
<p><strong>对外提供相应的接口</strong></p>
在面向对象设计过程中，有一些"套路”用于解决特定问题称为模式。
<p>DAO 模式提供了访问关系型数据库系统所需操作的接口，将数据访问和业务逻辑分离对上层提供面向对象的数据访问接口。</p>
<p>从以上 DAO 模式使用可以看出，DAO 模式的优势就在于它实现了两次隔离。</p>
<ul><li>1、隔离了数据访问代码和业务逻辑代码。业务逻辑代码直接调用DAO方法即可，完全感觉不到数据库表的存在。分工明确，数据访问层代码变化不影响业务逻辑代码,这符合单一职能原则，降低了藕合性，提高了可复用性。</li>
<li>2、隔离了不同数据库实现。采用面向接口编程，如果底层数据库变化，如由 MySQL 变成 Oracle 只要增加 DAO 接口的新实现类即可，原有 MySQ 实现不用修改。这符合 <strong>"开-闭"</strong> 原则。该原则降低了代码的藕合性，提高了代码扩展性和系统的可移植性。</li></ul>
<p><strong>一个典型的DAO 模式主要由以下几部分组成。</strong></p>
<ul><li>
1、DAO接口： 把对数据库的所有操作定义成抽象方法，可以提供多种实现。</li><li>
2、DAO 实现类： 针对不同数据库给出DAO接口定义方法的具体实现。</li><li>
3、实体类：用于存放与传输对象数据。</li><li>
4、数据库连接和关闭工具类： 避免了数据库连接和关闭代码的重复使用，方便修改。</li></ul>

<p><strong>DAO 接口:</strong></p>

<pre>public interface PetDao {
    /**
     * 查询所有宠物
     */
    List&lt;Pet&gt; findAllPets() throws Exception;
}</pre>

<p><strong>DAO 实现类:</strong></p>

<pre>public class PetDaoImpl extends BaseDao implements PetDao {
    /**
     * 查询所有宠物
     */
    public List&lt;Pet&gt; findAllPets() throws Exception {
        Connection conn=BaseDao.getConnection();
        String sql="select * from pet";
        PreparedStatement stmt= conn.prepareStatement(sql);
        ResultSet rs=    stmt.executeQuery();
        List&lt;Pet&gt; petList=new ArrayList&lt;Pet&gt;();
        while(rs.next()) {
            Pet pet=new Pet(
                    rs.getInt("id"),
                    rs.getInt("owner_id"),
                    rs.getInt("store_id"),
                    rs.getString("name"),
                    rs.getString("type_name"),
                    rs.getInt("health"),
                    rs.getInt("love"),
                    rs.getDate("birthday")
                    );
                petList.add(pet);
        }
        BaseDao.closeAll(conn, stmt, rs);
        return petList;
    }
}</pre>

<p>宠物实体类(里面get/set方法就不列出了)</p>

<pre>public class Pet {
    private Integer id;    
    private Integer ownerId;    //主人ID
    private Integer storeId;    //商店ID
    private String name;    //姓名
    private String typeName;    //类型
    private int health;    //健康值
    private int love;    //爱心值
    private Date birthday;    //生日
}</pre>

<p><strong>连接数据库</strong></p>

<pre>public class BaseDao {
    private static String driver="com.mysql.jdbc.Driver";
    private static String url="jdbc:mysql://127.0.0.1:3306/epet";
    private static String user="root";
    private static String password="root";
        static {
            try {
                Class.forName(driver);
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
        
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, user, password);    
    }
    
    public static void closeAll(Connection conn,Statement stmt,ResultSet rs) throws SQLException {
        if(rs!=null) {
            rs.close();
        }
        if(stmt!=null) {
            stmt.close();
        }
        if(conn!=null) {
            conn.close();
        }
    }
    

    public int executeSQL(String preparedSql, Object[] param) throws ClassNotFoundException {
        Connection conn = null;
        PreparedStatement pstmt = null;
        /* 处理SQL,执行SQL */
        try {
            conn = getConnection(); // 得到数据库连接
            pstmt = conn.prepareStatement(preparedSql); // 得到PreparedStatement对象
            if (param != null) {
                for (int i = 0; i &lt; param.length; i++) {
                    pstmt.setObject(i + 1, param[i]); // 为预编译sql设置参数
                }
            }
        ResultSet num = pstmt.executeQuery(); // 执行SQL语句
        } catch (SQLException e) {
            e.printStackTrace(); // 处理SQLException异常
        } finally {
            try {
                BaseDao.closeAll(conn, pstmt, null);
            } catch (SQLException e) {    
                e.printStackTrace();
            }
        }
        return 0;
    }
    
}</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="../note/27029">哈哈哈哈哈。。。呃~</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;哈哈哈哈哈。。。呃~</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;248***8117@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="../design-pattern/data-access-object-pattern.html">&nbsp;&nbsp;参考地址</a></p></div></span>5年前 (2018-05-07)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-34357"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;TiAmo</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;576***486@qq.com</p></div><div id="runoobvote-id-34357" data-commid = "34357" class="upvotejs"><a class="upvote"></a> <span class="count">27</span></div></div><div class="comt-main" id="div-comment-34357">


<p data-title="Java 连接 MySQL 数据库 8.0 以上版本说明"><strong>MySQL 8.0 以上版本:</strong></p>

<p>驱动包版本 <strong>mysql-connector-java-8.0.12.jar</strong>。</p>

<p>数据库 URL 需要声明是否使用 SSL 安全验证及指定服务器上的时区：</p>
<pre>static final String DB_URL = jdbc:mysql://localhost:3306/runoob?useSSL=false&amp;serverTimezone=UTC;
conn = DriverManager.getConnection(DB_URL,USER,PASS);</pre>

<p>原本的驱动器是:</p>

<pre>Class.forName("com.mysql.jdbc.Driver");</pre>
<p>在 IDEA 里面提示是:<strong>
Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary</strong></p>

<p>意思是说原本的驱动器不赞成 或者 是废弃了，自动换成了新的驱动器 com.mysql.cj.jdbc.Driver</p>

<pre>Class.forName("com.mysql.cj.jdbc.Driver");</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="../note/34357">TiAmo</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;TiAmo</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;576***486@qq.com</p></div></span>5年前 (2018-08-23)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-42451"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;this</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;tli***1990@gmail.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://juejin.im/post/5af952fdf265da0b9e652de3">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-42451" data-commid = "42451" class="upvotejs"><a class="upvote"></a> <span class="count">20</span></div></div><div class="comt-main" id="div-comment-42451"><p>在 JDBC4.0 之前，连接数据库的时候，通常会用 <code><strong>Class.forName("com.mysql.jdbc.Driver")</strong></code> 这句先加载数据库相关的驱动，然后再进行获取连接等的操作。而 JDBC4.0 之后不需要 <code>Class.forName</code> 来加载驱动，直接获取连接即可，这里使用了 Java 的SPI扩展机制来实现。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">this</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;this</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;tli***1990@gmail.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://juejin.im/post/5af952fdf265da0b9e652de3">&nbsp;&nbsp;参考地址</a></p></div></span>4年前 (2019-05-05)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-42694"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Nomoku</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;222***4847@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://my.oschina.net/gef/blog/712383">&nbsp;&nbsp;参考地址</a></p></div><div id="runoobvote-id-42694" data-commid = "42694" class="upvotejs"><a class="upvote"></a> <span class="count">15</span></div></div><div class="comt-main" id="div-comment-42694"><p>运行程序时抛出异常：</p>

<pre>Caused by: java.sql.SQLException: The server time zone value '�й���׼ʱ��' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the serverTimezone configuration property) to use a more specifc time zone value if you want to utilize time zone support.</pre>
<p><strong>解决办法：</strong></p>

<p>在</p>

<pre>jdbcUrl=jdbc:mysql://localhost:3306/spring</pre>
<p>后面加上：</p>

<pre>jdbcUrl=jdbc:mysql://localhost:3306/spring?serverTimezone=UTC  </pre>
<p>但如果你的 jdbcUrl 类似下面：</p>

<pre>jdbcUrl=jdbc:mysql://localhost:3306/spring?serverTimezone=UTC&amp;characterEncoding=utf-8</pre>
<p>就是有多个 params 的时候需要以 &amp; 分开，但 &amp; 要改为 &amp;amp; &nbsp;如下：</p> 

<pre>jdbcUrl=jdbc:mysql://localhost:3306/spring?serverTimezone=UTC&amp;characterEncoding=utf-8</pre>
<div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">Nomoku</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Nomoku</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;222***4847@qq.com</p><p><i class="fa fa-external-link" aria-hidden="true"></i> <a rel="nofollow" target="_blank" href="https://my.oschina.net/gef/blog/712383">&nbsp;&nbsp;参考地址</a></p></div></span>4年前 (2019-05-12)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-43516"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;baicai</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;420***699@qq.com</p></div><div id="runoobvote-id-43516" data-commid = "43516" class="upvotejs"><a class="upvote"></a> <span class="count">23</span></div></div><div class="comt-main" id="div-comment-43516"><p>使用 Maven 自动下载 mysql-connector-java。</p>

<p>在 maven 工程下的 pom.xml  中加mysql-connector-java 的依赖，只需要填想要的版本号，就能自动下载对应的 jar 包，更加方便。</p>


<pre>&lt;dependency&gt;
    &lt;groupId&gt;mysql&lt;/groupId&gt;
    &lt;artifactId&gt;mysql-connector-java&lt;/artifactId&gt;
    &lt;version&gt;8.0.16&lt;/version&gt;
&lt;/dependency&gt;</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">baicai</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;baicai</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;420***699@qq.com</p></div></span>4年前 (2019-06-10)</div></div></li><!-- #comment-## -->
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	var callback = function(data) {
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		var re = /^[1-9]+/;
		if (re.test(um_id)) { 
			var ajax_data = {
				_vote_action: _vote_action,
				action: "pinglun_zan",
				um_id: um_id,
				um_action: "ding"
			};
			//console.log(ajax_data);
			$.post(ajaxurl,ajax_data,function(status){
				//if(status.vote_num>999) {
				//	_voteHtml = '<span style="display: block; text-align: center;font-size: 20px; color: #6a737c; margin: 8px 0;">'+kFormatter(status.vote_num) +'</span>';
				//	$("#runoobvote-id-" + um_id + " .count").hide().after(_voteHtml);
				//}
				
			});
		}
	};
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				$("#runoobvote-id-" + value.commid + " .downvote").addClass(value.downvote_class);
				$("#runoobvote-id-" + value.commid + " .count").text(value.upvote_count);
			})
		},'json');
		
	}
	
	
});
function isBlank(str) {
    return (!str || /^\s*$/.test(str));
}
function kFormatter(num) {
	// return num;
    return Math.abs(num) > 999 ? Math.sign(num)*((Math.abs(num)/1000).toFixed(1)) + 'k' : Math.sign(num)*Math.abs(num)
}

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